Optimization of flocculation efficiency and settling time using chitosan and eggshell as bio-flocculant in Chlorella pyrenoidosa harvesting process

Abstract

The flocculation efficiency and settling time are important parameters to investigate the solid–liquid separation in the Chlorella pyrenoidosa microalgae harvesting process. A response surface methodology (RSM) with central composite design (CCD), was used to optimize flocculation efficiency and settling time parameters, where chitosan and egg shell used as bio-flocculant. The factors were chosen for bio-flocculant dose, pH and cationic inducer dose. Multiple response optimization was used effectively to estimate optimal parameters using the overall desirability function approach. The optimal flocculation efficiency of 93.33% and settling time of 112 s obtained when chitosan dosage of 53.17 mg/120 mL culture, pH of 8.99, and cationic inducer of 20.87 mg/L. On the other side, the optimal flocculation efficiency of 90.78% and settling time of 137 s obtained when eggshell dosage of 59.98 mg/120 mL culture, pH of 9.10, and cationic inducer of 21.11 mg/L. In chitosan and eggshell respectively as bio-flocculant, the flocculation rate was 3.491 and 1.819 min −1. After flocculation process, the dry weight of biomass floc was 0.767 and 0.486 grams, with chitosan and eggshell being bio-flocculent, respectively. This RSM-CCD approach for flocculation optimization will help to recycle water and to manage the process of microalgae harvesting.